The present invention relates to a device for preventing oscillation when no signals are supplied to a video cassette recorder (VCR). A switching circuit of the aural signal is formed in the interior of VCR so that oscillation by the noise signals of a feed back loop formed between the aural signal input and output terminals of VCR and TV does not take place when using a VCR and a television receiving set (TV) connected to each other. In general, a TV is designed to be used as a monitor by connecting the TV and the VCR with cables.
As shown in FIG. 1, TV 20 is, for example, designed to be used as a monitor by connecting the aural signal input and output terminals 22, 23, of TV to the aural signal input and output terminals 24, 25 of VCR 21 with cables. As shown in FIG. 2, however, if TV 20 is in a TV mode state such that the tuner/line transfer switch 26 of VCR 21 is transferred toward the point of contact (b) which is in a line state, a feedback loop is formed through the contact point (b) of tuner/line transfer switch 26 the amplifier 27 and the aural signal output terminal 25 of VCR 21, the aural signal input terminal 22, the sound circuit 28 and the aural signal output terminal 23 of TV 20, and the aural signal input terminal 24 of VCR 21. Since a noise signal is generated from such feedback circuit, and the noise signal is amplified and oscillated through the amplifier 27, the sound of the oscillation is output to the speaker of TV 20 even when both the VCR 21 and the TV 20 are in a no signal state.
Thus, according to such conventional device, there are problems created by the oscillation of the noise signal which may displease the audience and also a deterioration of the inner elements due to an excessive oscillation may result.